Devils Tower is a steep-sided igneous body and, possibly, an erosional remnant of a volcanic neck. It is made of magma that solidified at a shallow level (about 700 to 3,000 feet; 200 to 1000 m) below the surface. Erosion then stripped the overlying lay ers of rock away. The rock at Devils Tower is about 40 million years old. The rock is called a phonolite based on its mineral composition, which includes anorthoclase, aegirine-augite, and sphene. Devils Tower rises 1,253 feet (382 m) above the nearby Belle Fouche River. Photo by Steve Mattox, June 1979.

An impressive feature of Devils Tower is the columns joints that cut the monolith. Most of the columns are 5-sided and taper from 6.5-8 feet (2-2.5 m) at the base to about 4 feet (1.3 m) at the top. They formed as the magma cooled from the surface downw ard and from the periphery inward. Photo by Steve Mattox, June 1979.


Sources of Information:

Green, J. and Short, N.M., 1971, Volcanic landforms and surface features a photographic atlas and glossary: Springer Verlag, New York, 519 p.

Halvorson, D.L., 1980, Geology and petrology of the Devils Tower, Missouri Buttes, and Barlow Canyon area, Crook County, Wyoming: Grand Forks, University of North Dakota, Ph.D. dissertation, 218 p.

Karner, F.R., and Halvorson, D.L., 1987, The Devils Tower, Bear Lodge Mountains, Cenozoic igneous complex, in Beus, S.S., ed., Centennial Field Guide Volume 2 Rocky Mountain Section of the Geological Society of America, p. 161-164.

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United States